Preparation of 6-bromo-5-chloro-1H-indazole (Compound x23): To a solution of 5-bromo-4-chloro-2-methylaniline (1 g, 4.54 mmol) in acetic acid (10 mL) was slowly added dropwise a solution of sodium nitrite (0.329 g, 4.76 mmol) in water (1 mL). The reaction mixture was heated to reflux and maintained for 2 hours. Upon completion of the reaction, the mixture was cooled to room temperature and concentrated under reduced pressure to remove most of the solvent. The concentrated residue was dispersed in water and extracted with ethyl acetate (EtOAc). All organic phases were combined, washed with saturated brine and subsequently dried with anhydrous magnesium sulfate. After filtration to remove the drying agent, the filtrate was concentrated under reduced pressure to afford the title compound 6-bromo-5-chloro-1H-indazole (0.67 g, 64% yield) in the form of a reddish brown solid. It was analyzed by electrospray ionization mass spectrometry (ESI-MS) and the molecular ion peak [M + H]+ was measured as 232.2.
